This is a tricky one - since you might think that all fertilizers are more or less the same constitution of Nitrogen, Phosphorus and Potassium (NPK). However, the smaller micronutrients such as sulfur, calcium and magnesium can be very important for good growth of your plant.
In most cases, a normal all-around fertilizer does work - but sometimes you might need to make sure you are using the correct one. This is mostly important for flowering plants, or particularly sensitive plants - for example, carnivores such as venus fly traps or sundews (Drosera) can actually die if they are fertilized! Another example is geraniums - these are likely to stop flowering if they receive the wrong type of fertilizer, and orchids are prone to burnt roots and leaves as a consequence of this.
As a general rule, make sure not to use garden fertilizers on your indoor houseplants, as these will be too strong.
SIGNS OF INCORRECT FERTILIZER
Flowers fall off
Note! The above signs can also be caused by other issues with your plant.
WHAT TO DO NOW:
When you place a plant in a pot that doesn’t have any drainage holes, this can result in the fertilizer staying in the soil for too long. Having drainage holes in your plant pots can prevent this issue, as when you water, residues/salts will be flushed out of the soil, helping to prevent any harmful buildup.
However, when fertilizer residue does end up being trapped in the soil, this will lead to the plant never having the chance to be able to fully dry up, which can cause the root rot and may also lead to roots getting burned by the fertilizer.
To fix it:
Carefully dig up your plant from the pot- try to be particularly gentle with the roots
Remove as much old soil from your plant as possible
Repot your plant in a pot with holes and use a recommended soil for your plant
Cut back on fertilizing for a while- this will give your plant a chance to rest and recover. You can skip the fertilizing tasks in Planta for now
You can find all the info you need regarding the right soil and how to repot under the Info tab on the plant’s profile page
Remember to also register that you repotted your plant in Planta to update the care schedule (Open your plant’s profile and then press on the + button).
HOW TO PICK THE RIGHT FERTILIZER - A SHORT GUIDE
When choosing which type of fertilizer to use for your houseplants, the most important thing to keep in mind is the N-P-K ratio (Nitrogen- Phosphorus - Potassium) as these are the key nutrients that your plant needs. Where this ratio is a higher value, it means that the fertilizer is more concentrated, and therefore less is needed. However, these ratios should be well-balanced. Some fertilizers aso contain additional micronutrients - these are called ‘complete’ fertilizers. It’s important to choose a fertilizer that is formulated for houseplants specifically - it should state this on the packaging - as these have different N-P-K ratios to garden fertilizers. If you use a fertilizer that is not intended for houseplants, it will be too strong, and so you risk harming your plants.
Planta recommends using liquid fertilizer, as it is easy to use and generally priced affordably.
Some fertilizers are better than others - if possible, try to choose organic fertilizers over chemical fertilizers. Organic fertilizers contain all-natural ingredients and are the more eco-friendly option, whereas in chemical fertilizers, the nutrients are synthesized artificially. Chemical fertilizers also typically don’t contain any micronutrients, so are less beneficial for your plant overall. So, while some ‘bad’ fertilizers may be cheaper/more easily accessible, it’s worth spending a little extra money to get the best possible fertilizer for your houseplants.